Navigation systems are widely used in cars and other vehicles. The increasing popularity of navigation systems can be attributed to the enhanced comfort and increased security offered by such systems. Navigation systems may provide assistance in navigation tasks such as identifying an optimum route, identifying suitable route alternatives, or route guidance. Route guidance is one example of a driver assistance function. A driver may be informed when a lane change is required to follow a certain route. Other driver assistance functions may relate to security-related aspects, such as warning a driver when he is positioned on the wrong lane, warning the driver of a potentially dangerous intersection or other critical situations.
Driver assistance systems which help the driver in the driving process are also referred to as “Advanced Driver Assistance Systems” (ADAS). Examples for such advanced driver assistance functions include lane departure warnings, lane change assistance, or night vision, for example. Some advanced driver assistance function require the position of the vehicle to be determined with an accuracy which is less than a lane width in the transverse direction of a road, for example, to identify the lane on which a vehicle is presently located.
One approach for improving the position determining accuracy combines different position sensing techniques. For illustration, a combination of GPS and wheel speed sensor may be used to determine the position along a longitudinal direction of a road with higher accuracy.
Other approaches for improving the position determining accuracy may use a combination of data stored in a map database and image data captured with an image sensor. Approaches of this type may be used to identify lane markings, traffic signs, or other buildings in an image and to perform a matching between objects identified in an image and map data to refine a position estimate provided, for example, by a GPS system or other positioning system. Such conventional systems may suffer from reduced performance under poor lighting conditions, in particular during night time. The driver is in particular need for reliable driver assistance functions at night time when visual conditions are poor.